铁原子与氮分子间的相互作用——单侧双配位构型

用密度泛函理论的B3LYP/6-311+G(d)方法对单侧双配位FeN2体系(简记为S-FeN2)不同自旋多重度的稳定态、范德华力作用态和过渡态的多个电子态的几何结构、电子结构、能量和振动频率进行了计算比较研究. 结果表明, S-FeN2体系三种自旋态间, Fe—N 距离R1和N—N 距离R2值均比较接近; 能量最低的是15B2态, 相近态有15B1、13B1和13B2, 彼此能差约25 kJ·mol-1. 三重态电子结构复杂, 单重态能量普遍偏高; 基组态Fe原子与N2间存在强的σ-π电子对排斥而无有效轨道重叠和电子转移, 其它组态4s13d7、4s13d64p1和3d74p1, Fe 和N2间发生σ(sd)-π和π-π*轨道重叠作用, 有少量电子转移, 体系呈现一定的离子性特征, 活化N2键长基本不超过120 pm. Fe 原子的电子单或双重被激发到由N2反键轨道为主要成分的分子轨道上时, 能使N2活化到单键程度甚至解离.

Interaction of Iron Atom and Nitrogen Molecule——the Side-on Structure

The side-on bounded FeN2 (s-FeN2 for short) structure was calculated using B3LYP/6-311+G(d) method. The geometric structures, electronic structures, energies, and vibrational frequencies were calculated for many stable electronic states, van der Waals force interaction states, and transition states with different spin multiplicities. The results showed that: (1) the Fe—N bond length R1 and N—N bond length R2 were close to each other among the same kind states; (2) the fourmost stable electronic states of the side-on bounded FeN2were 15B2, 15B1, 13B1, and 13B2, the energy differences were about 25 kJ·mol-1; the electronic structures of the triplet states were plentiful, most of the singlet states were much higher in total energies than triplets’ and quintets’; (3) there have no fragment orbital overlap and electron transfer in S-FeN2 when Fe atom takes on 3d64s2 configuration due to the strong electron repulsion between σ or π electron pairs. To the other excited-state configurations 4s13d7, 4s13d64p1, and 3d74p1, there were some electrons transfer from Fe atom to N2 molecule via σ(sd)-π and π-π* orbitals overlap, the systems present somewhat ionicity and the bond length of activated N2 is generally not larger than 120 pm, that means Fe atom cannot insert into N≡N; (4) if electrons were excited to the molecular orbitals composed by nitrogen molecule moiety π-orbitals, the N2 could be activated to single bond even dissociation.